The present invention is directed to the pyrolysis of solid organic wastes from industrial and municipal sources and to obtaining a halide free pyrolytic oil therefrom.
The disposal of wastes both from municipal and industrial sources, such as trash, rubbish, garbage, animal wastes, agricultural wastes, and waste of plastic processing operations is rapidly becoming of immense national concern. The cost of disposal ranks third behind public schooling and highways as municipal expense in the United States.
It is estimated that each individual in the country generates between 4 and 6 pounds of waste per day, that the industrial output is equivalent to approximately 5 pounds of solid waste per person per day. Previous methods of mass waste disposal, such as landfill are becoming impossible, while others such as incineration are costly and result in air pollution problems.
A vast majority of the waste which is presently disposed of contains products which are immediately recycable back into the economy or products into which the waste can be converted for recycle back to the economy. Directly recyclable constituents are the various metals present, such as aluminum and steel, and glass. For the most part, the organic fraction of the waste is subject to a flash pyrolysis operation following recovery of the directly recyclable inorganic fraction. Flash pyrolysis yields a carbon containing solid residue of pyrolysis and a pyrolytic oil as products.
A particularly attractive method for converting the solid organic wastes into new and useful products consists of a process where the waste material is first dried and comminuted to a particle size wherein the largest particle has a maximum particle dimension of less than about 1 inch. There is then formed a turbulent gas stream by admixing the dried comminuted waste material with a solid source of heat and a carrier gas which does not deleteriously react with or oxidize the organic waste materials or products derived therefrom. The mixture is passed through a flash pyrolysis zone where at a temperature between 600 and 2000.degree. F. the organic waste undergo flash pyrolysis yielding a carbon containing solid residue of pyrolysis and a vaporized hydrocarbon constituent. The vaporized hydrocarbon constituent is separable as a pyrolytic oil and a normally gaseous hydrocarbon constituent which may be recycled to the process and, for instance, combusted to heat the solid source of heat or utilized because of its olefin content. A portion of the carbon containing solid residue of pyrolysis is normally recycled to provide the solid source of heat.
The pyrolytic oils formed while varying in nature depending upon the compositions of the waste material processed and pyrolysis conditions employed are at the same time unique. They may be characterized as an oxygenated, complex organic fluid, typically up to 40% soluble in water or acids, and almost completely soluble in bases. Solubility in polar organic solvents such as dimethyl formamide or dimethyl sulfoxide is high and the pyrolytic oils are relatively insoluble in non-polar organic solvents, such as diesel oil, carbon tetrachloride, pentane, decane, benzene, toluene and hexane. The pyrolysis oil, however, can be successively blended and mixed with various fuel oils, although it is not miscible with such fuel oils. Combustion stability of the mixture is about the same as #6 fuel oil alone.
A typical example of an elemental analysis of the pyrolytic oil is that obtained from the pyrolysis of a waste material containing about 70% cellulosics. The oil thus obtained will contain from about 52 to about 50% carbon, from about 6 to about 8% hydrogen, from about 1 to about 2% nitrogen and from about 29 to about 33% oxygen. The empirical formula which best fits the pyrolytic oil analysis is C.sub.5 H.sub.8 O.sub.2. Specific gravities are unusually high, ranging from about 1.5 to about 1.4.
Municipal and industrial wastes can contain various quantities of halides, the most conspicuous of which is chlorine. Chlorine sources range from plastics such as polyvinyl chloride to animal feed lot wastes. One municipality has estimated that the chlorine content of trash will range from 0.7 to about 1.8% by weight, with a mean estimate of 1.3%. Considering a 500 ton per day plant processing municipal waste, the potential hydrogen chloride output on the plant amounts to 6.7 tons per day.
Not only are the hydrogen halides such as hydrogen chloride worth recovering as the corresponding acid, they present problems of corrosion and secondary disposal problems from a pollution standpoint which must be coped with.
At the same time, hydrogen halides cannot be recovered as a component of the pyrolytic oil, since one of the principal end uses for the pyrolytic oil is as a fuel oil. Understandably, it would be desirable to have the vent gases from the combustion of the fuel essentially free of hydrogen halides from both a corrosion and pollution standpoint.